This invention relates to the fabrication of composite structures, and is particularly directed to a method for producing integrally stiffened panels formed of fiber reinforced resinous or plastic materials such as tapes of graphite impregated with epoxy resin.
It is desirable particularly in the aircraft industry, to provide lightweight structural components which have good structural integrity at reduced cost. In many instances structural components especially for the aircraft industry are in the form of a detailed multiple aluminum structure. It is thus desirable to replace such structures with one-piece or integral composite assembly to simplify the fabrication procedure, while maintaining structural integrity and reducing weight, and also reducing the cost of fabrication. Various procedures heretofore have been developed for the production of composite structural components, for example formed from fiber reinforced resin impregnated fabrics or tapes. Thus, U.S. Pat. Nos. 3,926,708; 3,939,024; 3,946,127; 3,959,544; 3,995,080; and 4,012,549 are illustrative of the production of various fiber reinforced composite structures employing, for example, fiber reinforced resin impregnated tape in a lay-up procedure, and employing molds or die in fabricating the structure. U.S. Pat. Nos. 4,062,917 and 3,126,582 disclose a method of making resin-impregnated fabric materials employing a rubber-like mold. However, when producing composite structures by the use of encapsulated rubber, very high internal pressures are encountered, which squeeze excessive amounts of resin from a layup, rendering it too dry for structural acceptance. U.S. Pat. Nos. 4,051,289 and 4,223,053 illustrate interconnection of panel-like members or face sheets with stiffening ribs of V-shaped configuration.
It is an object of the present invention to provide improved procedure for the fabrication of integrally stiffened composite panels formed of fiber reinforced composite material.
Another object is the provision of procedure for fabricating a one-piece or integrally stiffened panel formed of T-shaped stringers or stiffeners integrally connected to an outer skin.
A still further object is to provide unique assembling and molding procedure in a die, including the initial production of a rubber-like form block in the die, and functioning as a means for maintaining in position a plurality of T-shaped stringers or stiffeners, and supporting an outer skin in contact with such stringers, for co-curing the stringers and outer skin to form an integrally stiffened panel.
Yet another object is the provision of molding procedure as noted above, whereby the high initial pressure generated in a partially encapsulated rubber mold during the heating and bonding cycle in an autoclave, can be suitably controlled.